Human cytomegalovirus antagonizes activation of Fcγ receptors by distinct and synergizing modes of IgG manipulation

The pentameric complex is not required for congenital CMV transmission in seronegative rhesus macaques

Congenital cytomegalovirus (cCMV) is the leading infectious cause of neonatal neurological impairment worldwide, but the viral factors enabling vertical spread across the placenta remain undetermined. The pentameric complex (PC), composed of the subunits gH/gL/UL128/UL130/UL131A, has been demonstrated to be important for entry into nonfibroblast cells in vitro. These findings link the PC to broad cell tropism and virus dissemination in vivo, denoting all subunits as potential targets for intervention strategies and vaccine development. To determine the relevance of the PC for congenital transmission in a translational nonhuman primate model, we engineered a rhesus CMV (RhCMV) mutant lacking the orthologs of UL128 and UL130, which demonstrated diminished infection of epithelial cells in vitro. However, intravenous inoculation of either CD4+ T cell-depleted or immunocompetent RhCMV-seronegative pregnant rhesus macaques (RMs) in the early second trimester with the PC-deficient mutant resulted in maternal RhCMV peak plasma viremia similar to inoculations with PC-intact RhCMV, although virus shedding in saliva and urine was limited. Infections with the PC-intact virus induced IgG responses that neutralized RhCMV entry into epithelial cells in tissue culture. These responses were reduced, but not absent, from animals infected with the PC-deficient virus, which also induced IgG responses against gH. Moreover, congenital CMV transmission was confirmed in multiple animals infected with PC-deficient virus by detecting viral DNA in the amniotic fluid, indicating that transplacental transmission in RMs is not contingent on the PC.

Rhesus Cytomegalovirus-encoded Fcγ-binding glycoproteins facilitate viral evasion from IgG-mediated humoral immunity

Human cytomegalovirus (HCMV) encodes four viral Fc-gamma receptors (vFcγRs) that counteract antibody-mediated activation in vitro, but their role in infection and pathogenesis is unknown. To examine their in vivo function in an animal model evolutionarily closely related to humans, we identified and characterized Rh05, Rh152/151 and Rh173 as the complete set of vFcγRs encoded by rhesus CMV (RhCMV). Each one of these proteins displays functional similarities to their prospective HCMV orthologs with respect to antagonizing host FcγR activation in vitro. When RhCMV-naïve male rhesus macaques were infected with vFcγR-deleted RhCMV, peak plasma DNAemia levels and anti-RhCMV antibody responses were comparable to wildtype infections of both male and female animals. However, the duration of plasma DNAemia was significantly shortened in immunocompetent, but not in CD4 + T cell-depleted animals. Since vFcγRs were not required for superinfection of rhesus macaques, we conclude that these proteins can prolong lytic replication during primary infection by evading virus-specific adaptive immune responses, particularly antibodies.

Oncolytic cytomegaloviruses expressing EGFR-retargeted fusogenic glycoprotein complex and drug-controllable interleukin 12

Cytomegalovirus (CMV) infects a wide range of cell types, including tumor-associated myeloid cells and glioma cells. Clinical observations suggest a potential link between long-term glioblastoma survival and CMV reactivation. We herein present an oncolytic CMV vector, AD169r, which includes a restored pentamer complex gH/gL/pUL128-131 and the removal of UL1-UL20 and UL/b' sequences. The epidermal growth factor receptor (EGFR)-retargeted paramyxoviral glycoprotein H/F complexes are incorporated into AD169r backbone to enhance viral oncolysis. Additionally, a tet-off-controlled single-chain interleukin (IL)-12 is added to boost antitumor immune responses. The engineered oncolytic CMVs expressing EGFR-retargeted H/F complex demonstrate enhanced antitumor efficacy in human glioblastoma xenograft models. In the immunocompetent mouse CT-2A glioblastoma model, an oncolytic murine CMV (mCMV) expressing IL-12 significantly increases the abundance and cytotoxicity of CD4+ T cells, CD8+ T cells, and CD4-CD8- T cells in both treated and untreated tumors. Our findings highlight the potential of the AD169r-derived oncolytic viruses as CMV-based cancer viroimmunotherapy.

A vaccine against cytomegalovirus: how close are we?

The pursuit of a vaccine against the human cytomegalovirus (HCMV) has been ongoing for more than 50 years. HCMV is the leading infectious cause of birth defects, including damage to the brain, and is a common cause of complications in organ transplantation. The complex biology of HCMV has made vaccine development difficult, but a recent meeting sponsored by the National Institute of Allergy and Infectious Diseases in September of 2023 brought together experts from academia, industry, and federal agencies to discuss progress in the field. The meeting reviewed the status of candidate HCMV vaccines under study and the challenges in clinical trial design in demonstrating efficacy against congenital CMV infection or the reduction of HCMV disease following solid organ transplantation or hematopoietic stem cell transplantation. Discussion in the meeting revealed that, with the numerous candidate vaccines that are under study, it is clear that a safe and effective HCMV vaccine is within reach. Meeting attendees achieved a consensus opinion that even a partially effective vaccine would have a major effect on the global health consequences of HCMV infection.

Improving antibody-mediated protection against HSV infection by eliminating interactions with the viral Fc receptor gE/gI

Herpes simplex virus (HSV) encodes surface glycoproteins that are host defense evasion molecules, allowing the virus to escape immune clearance. In addition to their role in neuropathogenesis and cell-cell spread, glycoproteins E and I (gE/gI) form a viral Fc receptor (vFcR) for most subclasses and allotypes of human IgG and promote evasion of humoral immune responses. While monoclonal antibodies (mAbs) protect mice from neonatal HSV (nHSV) infections, the impact of the vFcR on mAb-mediated protection by binding to IgG is unknown. Using HSV-1 with intact and ablated gE-mediated IgG Fc binding, and Fc-engineered antibodies with modified ability to interact with gE/gI, we investigated the role of the vFcR in viral pathogenesis and mAb-mediated protection from nHSV. The gD-specific human mAb HSV8 modified to lack binding to gE exhibited enhanced neutralization and in vivo protection compared to its native IgG1 form. This improved protection by the engineered mAbs was dependent on the presence of the vFcR. Human IgG3 allotypes lacking vFcR binding also exhibited enhanced antiviral activity in vivo, suggesting that vaccines that robustly induce IgG3 responses could show enhanced protection. suggesting the value of vaccination strategies that robustly induce this subclass. Lastly, analysis of longitudinal responses to acute primary genital infection in humans raised the possibility that unlike most viruses, HSV may exhibited slow induction of IgG3. In summary, this study demonstrates that mAbs lacking the ability to interact with the vFcR can exhibit improved protection from HSV-offering new prospects for antibody-based interventions.

Receptor transfer between immune cells by autoantibody-enhanced, CD32-driven trogocytosis is hijacked by HIV-1 to infect resting CD4 T cells

Immune cell phenotyping frequently detects lineage-unrelated receptors. Here, we report that surface receptors can be transferred from primary macrophages to CD4 T cells and identify the Fcγ receptor CD32 as driver and cargo of this trogocytotic transfer. Filamentous CD32+ nanoprotrusions deposit distinct plasma membrane patches onto target T cells. Transferred receptors confer cell migration and adhesion properties, and macrophage-derived membrane patches render resting CD4 T cells susceptible to infection by serving as hotspots for HIV-1 binding. Antibodies that recognize T cell epitopes enhance CD32-mediated trogocytosis. Such autoreactive anti-HIV-1 envelope antibodies can be found in the blood of HIV-1 patients and, consistently, the percentage of CD32+ CD4 T cells is increased in their blood. This CD32-mediated, antigen-independent cell communication mode transiently expands the receptor repertoire and functionality of immune cells. HIV-1 hijacks this mechanism by triggering the generation of trogocytosis-promoting autoantibodies to gain access to immune cells critical to its persistence.

Rhesus Cytomegalovirus-encoded Fcγ-binding glycoproteins facilitate viral evasion from IgG-mediated humoral immunity

Human cytomegalovirus (HCMV) encodes four viral Fc-gamma receptors (vFcγRs) that counteract antibody-mediated activation in vitro , but their role in infection and pathogenesis is unknown. To examine the in vivo function of vFcγRs in animal hosts closely related to humans, we identified and characterized vFcγRs encoded by rhesus CMV (RhCMV). We demonstrate that Rh05, Rh152/151 and Rh173 represent the complete set of RhCMV vFcγRs, each displaying functional similarities to their respective HCMV orthologs with respect to antagonizing host FcγR activation in vitro . When RhCMV-naïve rhesus macaques were infected with vFcγR-deleted RhCMV, peak plasma viremia levels and anti-RhCMV antibody responses were comparable to wildtype infections. However, the duration of plasma viremia was significantly shortened in immunocompetent, but not in CD4+ T cell-depleted animals. Since vFcγRs were not required for superinfection, we conclude that vFcγRs delay control by virus-specific adaptive immune responses, particularly antibodies, during primary infection.

Insights into the Transcriptome of Human Cytomegalovirus: A Comprehensive Review

Human cytomegalovirus (HCMV) is a widespread pathogen that poses significant risks to immunocompromised individuals. Its genome spans over 230 kbp and potentially encodes over 200 open-reading frames. The HCMV transcriptome consists of various types of RNAs, including messenger RNAs (mRNAs), long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), and microRNAs (miRNAs), with emerging insights into their biological functions. HCMV mRNAs are involved in crucial viral processes, such as viral replication, transcription, and translation regulation, as well as immune modulation and other effects on host cells. Additionally, four lncRNAs (RNA1.2, RNA2.7, RNA4.9, and RNA5.0) have been identified in HCMV, which play important roles in lytic replication like bypassing acute antiviral responses, promoting cell movement and viral spread, and maintaining HCMV latency. CircRNAs have gained attention for their important and diverse biological functions, including association with different diseases, acting as microRNA sponges, regulating parental gene expression, and serving as translation templates. Remarkably, HCMV encodes miRNAs which play critical roles in silencing human genes and other functions. This review gives an overview of human cytomegalovirus and current research on the HCMV transcriptome during lytic and latent infection.

Outsmarting Pathogens with Antibody Engineering

There is growing interest in identifying antibodies that protect against infectious diseases, especially for high-risk individuals and pathogens for which no vaccine is yet available. However, pathogens that manifest as opportunistic or latent infections express complex arrays of virulence-associated proteins and are adept at avoiding immune responses. Some pathogens have developed strategies to selectively destroy antibodies, whereas others create decoy epitopes that trick the host immune system into generating antibodies that are at best nonprotective and at worst enhance pathogenesis. Antibody engineering strategies can thwart these efforts by accessing conserved neutralizing epitopes, generating Fc domains that resist capture or degradation and even accessing pathogens hidden inside cells. Design of pathogen-resistant antibodies can enhance protection and guide development of vaccine immunogens against these complex pathogens. Here, we discuss general strategies for design of antibodies resistant to specific pathogen defense mechanisms.

Human immunoglobulins are transported to HCMV viral envelope by viral Fc gamma receptors-dependent and independent mechanisms

Human cytomegaloviruses (HCMVs) employ many different mechanisms to escape and subvert the host immune system, including expression of the viral IgG Fcγ receptors (vFcγRs) RL11 (gp34), RL12 (gp95), RL13 (gpRL13), and UL119 (gp68) gene products. The role of vFcγRs in HCMV pathogenesis has been reported to operate in infected cells by interfering with IgG-mediated effector functions. We found that gp34 and gp68 are envelope proteins that bind and internalize human IgGs on the surface of infected cells. Internalized IgGs are then transported on the envelope of viral particles in a vFcR-dependent mechanism. This mechanism is also responsible for the incorporation on the virions of the anti-gH neutralizing antibody MSL-109. Intriguingly, we show that gp68 is responsible for MSL-109 incorporation, but it is dispensable for other anti-HCMV antibodies that do not need this function to be transported on mature virions. HCMV-infected cells grown in presence of anti-HCMV monoclonal antibodies generate a viral progeny still infective and possible to be neutralized. This is the first example of a virus carrying neutralizing IgGs on its surface and their possible role is discussed.

Circulating multimeric immune complexes contribute to immunopathology in COVID-19

A dysregulated immune response with high levels of SARS-CoV-2 specific IgG antibodies characterizes patients with severe or critical COVID-19. Although a robust IgG response is considered to be protective, excessive triggering of activating Fc-gamma-receptors (FcγRs) could be detrimental and cause immunopathology. Here, we document excessive FcγRIIIA/CD16A activation in patients developing severe or critical COVID-19 but not in those with mild disease. We identify two independent ligands mediating extreme FcγRIIIA/CD16A activation. Soluble circulating IgG immune complexes (sICs) are detected in about 80% of patients with severe and critical COVID-19 at levels comparable to active systemic lupus erythematosus (SLE) disease. FcγRIIIA/CD16A activation is further enhanced by afucosylation of SARS-CoV-2 specific IgG. Utilizing cell-based reporter systems we provide evidence that sICs can be formed prior to a specific humoral response against SARS-CoV-2. Our data suggest a cycle of immunopathology driven by an early formation of sICs in predisposed patients. These findings suggest a reason for the seemingly paradoxical findings of high antiviral IgG responses and systemic immune dysregulation in severe COVID-19. The involvement of circulating sICs in the promotion of immunopathology in predisposed patients opens new possibilities for intervention strategies to mitigate critical COVID-19 progression.

During viral infections high levels of antibodies can form soluble immune complexes (sICs) with antigen and trigger Fcγ receptors (FcγR) leading to increased immunopathology. Here the authors measure FcγRs activation by sICs and consider how these may lead to excessive immunopathology during severe SARS-CoV-2 infection.

Antibody escape and global spread of SARS-CoV-2 lineage A.27

In spring 2021, an increasing number of infections was observed caused by the hitherto rarely described SARS-CoV-2 variant A.27 in south-west Germany. From December 2020 to June 2021 this lineage has been detected in 31 countries. Phylogeographic analyses of A.27 sequences obtained from national and international databases reveal a global spread of this lineage through multiple introductions from its inferred origin in Western Africa. Variant A.27 is characterized by a mutational pattern in the spike gene that includes the L18F, L452R and N501Y spike amino acid substitutions found in various variants of concern but lacks the globally dominant D614G. Neutralization assays demonstrate an escape of A.27 from convalescent and vaccine-elicited antibody-mediated immunity. Moreover, the therapeutic monoclonal antibody Bamlanivimab and partially the REGN-COV2 cocktail fail to block infection by A.27. Our data emphasize the need for continued global monitoring of novel lineages because of the independent evolution of new escape mutations.

Detection and functional resolution of soluble immune complexes by an FcγR reporter cell panel

Fc-gamma receptor (FcγR) activation by soluble IgG immune complexes (sICs) represents a major mechanism of inflammation in certain autoimmune diseases such as systemic lupus erythematosus (SLE). A robust and scalable test system allowing for the detection and quantification of sIC bioactivity is missing. We developed a comprehensive reporter cell panel detecting activation of FcγRs. The reporter cell lines were integrated into an assay that enables the quantification of sIC reactivity via ELISA or a faster detection using flow cytometry. This identified FcγRIIA(H) and FcγRIIIA as the most sIC-sensitive FcγRs in our test system. Reaching a detection limit in the very low nanomolar range, the assay proved also to be sensitive to sIC stoichiometry and size reproducing for the first time a complete Heidelberger-Kendall curve in terms of immune receptor activation. Analyzing sera from SLE patients and mouse models of lupus and arthritis proved that sIC-dependent FcγR activation has predictive capabilities regarding severity of SLE disease. The assay provides a sensitive and scalable tool to evaluate the size, amount, and bioactivity of sICs in all settings.

Human genetic polymorphisms and risk of viral infection after solid organ transplantation

The immune system plays a key role in the host defense against viral pathogens. A signaling cascade is activated upon infection involving a variety of molecules such as pattern-recognition receptors (PRRs), interleukins or antiviral interferons. Long-term immunosuppression after solid organ transplantation (SOT) mainly abrogates adaptive T-cell-mediated responses, thus highlighting the relative contribution of innate immunity. Single-nucleotide polymorphisms (SNPs) within genes coding for PRRs or soluble mediators have been associated with differential susceptibility to viral infections among SOT recipients. A protective effect against cytomegalovirus (CMV) infection or disease has been attributed to certain SNPs in TLR9 or IFNL3 genes, whereas the opposite effect has been attributed to genetic polymorphisms in TLR2, MBL2, DC-SIGN, IL10 or IFNG. The presence of SNPs in other molecules not directly involved in innate or adaptive immune responses such as aquaporins or pregnane X appear to modulate the risk of CMV or BK polyomavirus infection, respectively. Little information is available on the genetic determinants of the post-transplant susceptibility to herpesviruses causing clinical infection (herpes simplex virus or varicella zoster virus) or the replication kinetics of components of the human blood virome used as immune surrogates (Torque teno virus). The present review critically summarizes the current knowledge on how SNP genotyping would be useful to stratify SOT recipients according to the individual risk of viral infection and proposes next research steps. Genetic susceptibility testing may improve personalized medicine and contribute to minimize the risk of viral infection after SOT.

Analysis and Fine Specificity of the HCMV-Specific Cell-Free and Cell-Associated Antibody-Dependent Cellular Phagocytosis (ADCP) Responses in Lung Transplant Recipients

Human Cytomegalovirus (HCMV) may cause severe infections in transplant recipients. HCMV-replication can be limited by HCMV-specific antibody responses. The impact of the antibody-dependent cellular phagocytosis (ADCP) on inhibition of HCMV-replication in natural infections has not been clarified. Therefore, we investigated the HCMV-specific ADCP response in a study cohort of lung-transplant recipients (LTRs) with different donor (D) and recipient (R) HCMV-serostatus. Follow-up plasma samples from 39 non/low-viremic and 36 highly viremic (>1000 HCMV copies/mL plasma) LTRs were collected for one (R+ LTRs) or two (D+/R− LTRs) years post-transplantation. The HCMV-specific ADCP responses were assessed by focal expansion assays (FEA) and flow-cytometry. In all LTRs, ADCP responses were detected against HCMV-infected cells and cell-free virions. When measured in fibroblasts as well as with cell-free virus, the HCMV-specific ADPC response was higher in LTRs than in HCMV-seropositive healthy controls. In D+/R− LTRs, a significant ADCP response developed over time after the receipt of an HCMV positive lung, and a level of <19 IE⁺ cells/focus in the FEA on fibroblasts was associated with further protection from high-level viremia. Taken together, a strong HCMV-specific ADCP response is elicited in transplant recipients, which may contribute to protection from high-level viremia in primary HCMV infection.